CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
CURRENT ASSETS
Cash and cash equivalents	$ 64,991	$ 13,892
Customer and other receivables	370,714	305,147
Accrued unbilled revenues	196,373	112,434
Allowance for doubtful accounts	(5,215)	(2,513)
Materials and supplies (at average cost)	268,184	264,012
Fossil fuel (at average cost)	40,398	25,258
Assets from risk management activities (Note 7)	1,224	1,931
Deferred fuel and purchased power regulatory asset (Note 4)	65,726	75,637
Other regulatory assets (Note 4)	143,849	172,451
Other current assets	60,946	48,039
Total current assets	1,207,190	1,016,288
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Note 12)	906,687	871,000
Other special use funds (Note 12)	233,740	32,542
Other assets	106,988	52,040
Total investments and other assets	1,247,415	955,582
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	18,443,985	17,798,061
Accumulated depreciation and amortization	(6,328,751)	(6,128,535)
Net	12,115,234	11,669,526
Construction work in progress	1,200,625	1,291,498
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	106,743	109,645
Intangible assets, net of accumulated amortization	268,630	257,189
Nuclear fuel, net of accumulated amortization	134,812	117,408
Total property, plant and equipment	13,826,044	13,445,266
DEFERRED DEBITS
Regulatory assets (Note 4)	1,221,293	1,202,302
Assets for other postretirement benefits (Note 5)	29,094	268,978
Other	140,919	130,666
Total deferred debits	1,391,306	1,601,946
TOTAL ASSETS	17,671,955	17,019,082
CURRENT LIABILITIES
Accounts payable	249,059	256,442
Accrued taxes	226,846	148,946
Accrued interest	53,021	56,397
Common dividends payable	0	77,667
Short-term borrowings (Note 3)	128,200	95,400
Current maturities of long-term debt (Note 3)	600,000	82,000
Customer deposits	89,916	70,388
Liabilities from risk management activities (Note 7)	45,504	59,252
Liabilities for asset retirements	13,000	4,745
Regulatory liabilities (Note 4)	159,788	100,086
Other current liabilities	169,454	246,529
Total current liabilities	1,734,788	1,197,852
DEFERRED CREDITS AND OTHER
Deferred income taxes	1,813,472	1,690,805
Regulatory liabilities (Note 4)	2,410,597	2,452,536
Liabilities for asset retirements	682,389	674,784
Liabilities for pension benefits (Note 5)	316,423	327,300
Liabilities from risk management activities (Note 7)	34,226	37,170
Customer advances	125,267	113,996
Coal mine reclamation	210,030	231,597
Deferred investment tax credit	198,178	205,575
Unrecognized tax benefits	11,896	13,115
Other	161,464	148,909
Total deferred credits and other	5,963,942	5,895,787
COMMITMENTS AND CONTINGENCIES (SEE NOTE 8)
EQUITY
Common stock, no par value; authorized 150,000,000 shares, 112,015,949 and 111,816,170 issued at respective dates	2,629,627	2,614,805
Treasury stock at cost; 17,368 and 64,463 shares at respective dates	(1,409)	(5,624)
Total common stock	2,628,218	2,609,181
Retained earnings	2,780,428	2,442,511
Accumulated other comprehensive loss	(55,074)	(45,002)
Total shareholders’ equity	5,353,572	5,006,690
Noncontrolling interests (Note 6)	132,289	129,040
Total equity	5,485,861	5,135,730
Long-term debt less current maturities (Note 3)	4,487,364	4,789,713
TOTAL LIABILITIES AND EQUITY	17,671,955	17,019,082
APS
CURRENT ASSETS
Cash and cash equivalents	64,825	13,851
Customer and other receivables	350,028	292,791
Accrued unbilled revenues	196,373	112,434
Allowance for doubtful accounts	(5,215)	(2,513)
Materials and supplies (at average cost)	268,184	262,630
Fossil fuel (at average cost)	40,398	25,258
Assets from risk management activities (Note 7)	1,224	1,931
Deferred fuel and purchased power regulatory asset (Note 4)	65,726	75,637
Other regulatory assets (Note 4)	143,849	172,451
Other current assets	41,196	41,055
Total current assets	1,166,588	995,525
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Note 12)	906,687	871,000
Other special use funds (Note 12)	233,740	30,358
Other assets	40,710	36,796
Total investments and other assets	1,181,137	938,154
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	18,440,499	17,654,078
Accumulated depreciation and amortization	(6,325,513)	(6,041,965)
Net	12,114,986	11,612,113
Construction work in progress	1,200,625	1,266,636
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	106,743	109,645
Intangible assets, net of accumulated amortization	268,474	257,028
Nuclear fuel, net of accumulated amortization	134,812	117,408
Total property, plant and equipment	13,825,640	13,362,830
DEFERRED DEBITS
Regulatory assets (Note 4)	1,221,293	1,202,302
Assets for other postretirement benefits (Note 5)	25,455	265,139
Other	129,026	129,801
Total deferred debits	1,375,774	1,597,242
TOTAL ASSETS	17,549,139	16,893,751
CURRENT LIABILITIES
Accounts payable	241,548	247,852
Accrued taxes	263,521	157,349
Accrued interest	50,416	55,533
Common dividends payable	0	77,700
Current maturities of long-term debt (Note 3)	600,000	82,000
Customer deposits	89,916	70,388
Liabilities from risk management activities (Note 7)	45,504	59,252
Liabilities for asset retirements	13,000	4,192
Regulatory liabilities (Note 4)	159,788	100,086
Other current liabilities	165,206	243,922
Total current liabilities	1,628,899	1,098,274
DEFERRED CREDITS AND OTHER
Deferred income taxes	1,834,691	1,742,485
Regulatory liabilities (Note 4)	2,410,597	2,452,536
Liabilities for asset retirements	682,389	666,527
Liabilities for pension benefits (Note 5)	296,987	306,542
Liabilities from risk management activities (Note 7)	34,226	37,170
Customer advances	125,267	113,996
Coal mine reclamation	210,030	215,830
Deferred investment tax credit	198,178	205,575
Unrecognized tax benefits	41,673	43,876
Other	139,907	133,779
Total deferred credits and other	5,973,945	5,918,316
COMMITMENTS AND CONTINGENCIES (SEE NOTE 8)
EQUITY
Total common stock	178,162	178,162
Additional paid-in capital	2,571,696	2,571,696
Retained earnings	2,909,180	2,533,954
Accumulated other comprehensive loss	(33,756)	(26,983)
Total shareholders’ equity	5,625,282	5,256,829
Noncontrolling interests (Note 6)	132,289	129,040
Total equity	5,757,571	5,385,869
Long-term debt less current maturities (Note 3)	4,188,724	4,491,292
Total capitalization	9,946,295	9,877,161
TOTAL LIABILITIES AND EQUITY	$ 17,549,139	$ 16,893,751